Chemical Immobilization: Medical Emergencies 2 - Myopathy & Thermoregulation
The capture of wild animals is a highly stressful event which has the potential to cause capture-induced complications, some of which can result in morbidity or mortality. There are a number of zoological societies, universities and other organizations that offer education in safe capture chemical immobilization techniques for those who are interested in or who are pursuing careers in veterinary medicine, wildlife management, biology, zoology, animal control or continuing education credit. The purpose of these programs is to provide guidance regarding the safe chemical immobilization of animals, thereby reducing the likelihood of complications.
Through the San Diego Zoo Wildlife Alliance (SDZWA), the Zoological Society of San Diego currently offers coursescovering the principles of and techniques relating to chemical immobilization, pharmacology and drug delivery systems. One of the modules in this series is Chemical Immobilization: Medical Emergencies 2 - Myopathy & Thermoregulation.
Capture Myopathy
Capture myopathy is a serious condition that can occur in wild and domestic animals wherein muscle damage results from extreme exertion, struggle, or stress. It is also known as exertional myopathy, overstraining disease and exertional rhabdomyolysis.1 Capture myopathy most often occurs as a result of capture, transport or chemical immobilization, but it can also be the result of other natural causes of stress, such as in prey animals attempting to avoid or struggling with predator animals.2 It is of particular concern in cases when it is a cause of death in wild animals that are handled by humans.
Capture myopathy can occur naturally when animals are attempting to avoid predation, but capture myopathy is more often the result of animals being captured and/or immobilized with or without chemical means being involved. When animals overexert themselves (e.g., struggling in a trap or attempting to flee a capture team) to the extent that physiological imbalances develop and result in severe muscle damage, capture myopathy results.1 Increased ambient temperatures and repeated chemical immobilization can increase the risk of animals suffering from capture myopathy.2
Clinical signs of capture myopathy can vary depending on the species and the cause of exertion.2 The method of capture and restraint is also a determinant in occurrences of capture myopathy. The clinical signs during early onset include elevated respiratory rate, heart rate, and body temperature.1,3 Body temperature increases during exertion, with higher temperatures being associated with death due to capture myopathy. The increase in body temperature can be above 42°C.4Muscle spasms, stiffness and lameness are also clear signs of CM. Animals often become recumbent and may stumble. If dark red-colored urine is noted, this is an indication that the animal's muscles are breaking down and that its kidneys have been severely affected.2-4 Death of the animal usually follows.
There is no treatment for capture myopathy, prevention being the best method of avoiding this condition. Care should be taken in case of handling of animals that tend to be more susceptible to capture myopathy. An anesthetic protocol consisting of good anesthetic agents can aid significantly in preventing capture myopathy.
Thermoregulation: Stress, Hypothermia and Hyperthermia
The mechanisms underlying the increase in body temperature during capture-induced hypothermia and hyperthermia are not fully understood, but one factor appears to be the sympathetic stress response. Even with animals engaging in low levels of activity during capture with mild ambient temperatures can develop severe hyperthermia.5
Measurement of body temperature should be standard procedure during all anesthetic events, and thermometers should be able to read over a wide temperature range. Hypothermia is more common in small animals because of the large surface area-to-volume ratio, but instances of both hypothermia and hyperthermia have both been reported during the capture of large animals. Some drugs used in chemical immobilization are believed to suppress normal thermoregulatory mechanisms, thereby causing hypothermia or hyperthermia. Hyperthermia however, is also common immediately after immobilization of both captive and free-ranging animals due to excitement and struggling while darting.5-7
Monitoring core body temperature is essential during anesthesia,3,5 and intubation has been widely recommended for any anesthetized animal that needs to be transported or anesthetized for greater than one hour.
Treating Hyperthermia
Given that capture-induced hyperthermia in some animals may be severe, one method recommended for improving their chances for survival is to physically cool captured animals. Recommendations for cooling larger animals include placing them in the shade and dousing them with water using portable mist sprayers, followed by rapid intravenous (IV) fluid therapy.5 In animals with body temperatures greater than 41°C, the use of cold water enemas and intravenous infusion of cold Ringer’s lactate has been recommended.5,7
Ice packs were also reported to have restored the body temperature of hyperthermic animals to pre-capture levels.5 The authors point out however, that since carrying water is far less cumbersome and difficult than transporting and maintaining ice-packs in the field, thus they recommend that water-dousing is the most practical and effective first intervention for cooling an animal with capture-induced hyperthermia.
Treating Hypothermia
Hypothermia during anesthetic events is a common adverse effect of anesthesia in many species. In particular, smaller animals are susceptible to hypothermia during anesthetic events, but large hoofstock and even carnivores can be affected.7Thus, having thermal support available in the form of external heating devices during and after anesthesia is prudent. In general, the time of recovery from anesthesia is typically longer in case of injectable anesthesia rather than inhalant anesthesia.
Hypothermia can be reversed through the use of water bottles filled with warm water and placed around the animal’s body. External heating devices may also be used, although some of the literature states that heating pads should be used with care, as it is easy to burn an animal’s skin.7 Returning the animal to a warm environment (if possible) and/or using heat lamps (if available) can also be helpful.
The team in the field should be thoroughly aware of the risks of capture myopathy and thermoregulatory complications during chemical immobilization events, and make every effort to prevent their occurrence. Wild species should only be captured when necessary, and the negative effects that capture may have on an animal's health should always be considered before beginning a capture or initiating an anesthetic event.9 Capture methods that minimize animal stress, struggling and handling time should be utilized. Appropriate methods may vary depending on the species, so research can be helpful in identifying the ideal capture method.
Interested in learning more about safe capture? The San Diego Zoo now offers courses in safe capture techniques and best practices. Learn reliable, safe, and effective techniques for the species you work with and the scenarios you encounter!
1Williams, E. S., Thorne, E. T. 1996. Exertional Myopathy (Capture Myopathy). Noninfectious Diseases of Wildlife, Second Edition, 181-193 Iowa State University Press, Ames, Iowa, USA.
2Friend, M., Thomas, N. J. Field Manual of Wildlife Diseases. In: Field Manual of Wildlife Diseases, United States Geological Survey, 361-368.
3Blumstein, D., et. al. The evolution of capture myopathy in hooved mammals: a model for human stress cardiomyopathy?Evolution, medicine, and public health vol. 2015,1 195-203. 21 Jul. 2015,
4Businga NK, Langenberg J, Carlson L. Successful treatment of capture myopathy in three wild greater sandhill cranes (Grus canadensis tabida). J Avian Med Surg. 2007 Dec;21(4):294-8. doi: 10.1647/2005-013R1.1. PMID: 18351009.
5Sawicka, J. et. al. Efficacy of Different Cooling Methods for Capture-Induced Hyperthermia in Antelope. (2015).
6Haskins, S.C. (1995). Thermoregulation, hypothermia, hyperthermia. In: SJ. Ettinger. & EC. Feldman (Eds), Veterinary internal medicine (4th edition) (pp. 26–30). Philadelphia. U.S.A. W.B Saunders Company.
7Arnemo, J., Fahlman, A. (2008). Biomedical protocols for the free-ranging brown bears, gray wolves, wolverines and lynx. Hedmark University College, Norway and Swedish University of Agriculture Sciences, Sweden.
8Arnemo, Jon & Kreeger, Terry. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007.
9Richardson, D. Journal of Mammalogy, Volume 56, Issue 3, 29 August 1975, Pages 698–699.
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